1. Field of the Invention
The present invention relates to a servo control system of a disk drive using a disk as a recording medium and, more particularly, to a method of estimating the gain of a servo control system for controlling the position of a head which reads or writes data on a disk.
2. Description of the Related Art
Disk drives using a disk as a recording medium have been widely used as an auxiliary recording device of a computer system. A hard disk drive is a typical disk drive. The hard disk drive records data transmitted from a host computer on a predetermined track of the disk, and then reproduces and outputs the recorded data when a user demands it. That is, the main function of the hard disk drive is to read or write data.
In order to record data transmitted from the host computer on a predetermined track or to reproduce the recorded data from the track, first of all, the head must be located on the track. For this, a servo control is used for controlling the position and speed of the head. That is, the disk drive must include an element for carrying out reading and writing of data, and a servo controller for controlling the head before the reading and writing of data.
In a disk drive, a microprocessor is connected to a programmable read only memory and a static random access memory. A head is connected to one end of an actuator and effects a lateral movement on a disk of a recording medium and reads and writes data on the disk. A voice coil motor located on the other end of the actuator is vertically driven on the disk in response to the level and direction of the current supplied thereto. A spindle motor rotates the disk mounted on a driving axis in response to a control signal supplied from a motor driver. A voice coil motor driver connected to the voice coil motor controls the voice coil motor. A digital-to-analog converter which is connected to the microprocessor and the voice coil motor driver receives a digital control input signal from the microprocessor, converts it to an analog signal, and outputs it to the voice coil motor driver. The motor driver is connected to the spindle motor and microprocessor and controls the spindle motor under the control of the microprocessor.
A preamplifier connected to the head amplifies a read signal and outputs an input signal to be written by the head. A read/write channel circuit is connected to the microprocessor, preamplifier, and interface controller, and receives and encodes the written data from the interface controller and outputs it to the preamplifier under the control of the microprocessor. The read/write channel circuit digitally converts an analog read signal input from the preamplifier and outputs it as an encoded read data. An analog-to-digital converter is connected to the read/write channel circuit and receives an analog servo read signal and digitally converts it to a position error signal and outputs it to the microprocessor. A gate array connected to the read/write channel circuit receives the encoded read data and detects servo information such as a gray code in the servo region of the disk from the encoded read data.
In the aforementioned disk drive, the analog-to-digital converter, digital-to-analog converter, voice coil motor driver, and voice coil motor form one servo control system. Each element of the servo control system has a typical gain characteristic and accordingly, calibration during the servo control is obtained by measuring these characteristics when the drive is initially driven. That is, there are differences in the torque and inertia of the actuators between the disk drive sets and they can be changed by the surrounding temperature in the track seek mode of the disk drive. Furthermore, the gain of the digital-to-analog converter and analog-to-digital converter may be different between sets and changed by circumstances. Accordingly, a gain constant of the whole servo control system including the torque constant and inertia of the actuator, the gain constant of the digital-to-analog converter and the gain constant of the analog-to-digital converter are different between disk drive sets and can be variously changed according to environmental factors. In order to obtain the control performance of the servo control system which can overcome the environmental factors, the gain of the whole servo control system must be estimated all the time and automatically controlled. Accordingly, it is important to develop an algorithm for estimating the gain of the servo control system.
The transfer function of a servo control system is related to the torque constant of the voice coil motor, the inertia of the actuator, the gain constant of the digital-to-analog and analog-to-digital converters, and the sampling time. The microprocessor supplies a DC torque to an actuator to measure the speed during sampling and performs the estimation calculation employing control input data and output data as inputs to thereby output the gain estimate of the servo control system.
When a track is sought, since the DC torque is supplied during the acceleration section, the gain of the servo control system can be estimated at every track seek and thus, the control performance which can overcome the environmental variations can be obtained.
However, in the control system of the earlier disk drive, its speed is measured by differentiating the position data in order to obtain the output information of plant and this deteriorates the gain estimating performance of the servo control system if there is speed measurement noise. Furthermore, since the settling time of a power amplifier serving as a current controller is not considered in the earlier servo control system, the gain estimating performance of the servo control system is deteriorated.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited method of estimating the gain of a servo control system for controlling the position of a head which reads or writes data on a disk in accordance with the present invention: U.S. Pat. No. 5,483,439 to Ono et al., entitled Digital Servo Control System, U.S. Pat. No. 5,610,487 to Hutsell, entitled Servo System With Once Per Revolution Rejection, U.S. Pat. No. 5,347,447 to Kiji et al., entitled Adaptive Control System And Method Thereof U.S. Pat. No. 5,155,422 to Sidman et al., entitled Self-Tuning Adaptive Bandwidth Regulator, U.S. Pat. No. 4,983,898 to Kanda, entitled Method And System For Changing Control Parameters In Accordance With State Of Process In Process Control, U.S. Pat. No. 4,965,501 to Hashimoto, entitled servo Circuit, U.S. Pat. No. 4,882,526 to lino et al, entitled Adaptive Process Control System, U.S. Pat. No. 4,697,127 to Stich et al., entitled Adaptive Control Technique For A Dynamic System, U.S. Pat. No. 5,576,909 to Dierkes et al., entitled Method For Positioning A Data Transducer Head In A Rotating Disk Drive Data Storage Device, U.S. Pat. No. 5,521,771 to Keithley et al., entitled Servo Gain Compensation In A Disk Drive, U.S. Pat. No. 5,404,255 to Kobayashi et al., entitled Disk Apparatus And Its Control Method, and U.S. Pat. No. 5,585,976 to Pham, entitled Digital Sector Servo Incorporating Repeatable Run Out Tracking.